1. Field of the Invention
The present invention relates to a circuit board and, more particularly, to a circuit board having mesh-shaped earth (ground) lines.
2. Description of the Related Art
The circuit board having the mesh-shaped earth lines is suitable to install integrated circuits which operate at high speeds. This is because when the mesh-shaped earth lines are used, the electrostatic capacity between the signal line and the earth line is smaller than that in the case of using a sheet-shaped earth layer.
When the mesh-shaped earth lines are used, electrostatic capacity C between the earth line and the signal line differs on the position on the signal line. For example, in the crossing portion of the signal line and the earth lines, electrostatic capacity C between them is large. In the other portions of the signal line and the earth line, capacity C is relatively small. When electrostatic capacity C is not constant on the signal line, the characteristic impedance ##EQU1## is not constant on the signal line as well. Therefore, the conventional circuit board having the mesh-shaped earth lines has drawbacks such that if an impedance mismatching occurs on the signal line, the signal propagation characteristics will be poor.